Combustion of fossil fuels typically produces an exhaust gas stream (commonly referred to as a “flue gas stream”) that contains contaminants, such as sulfur oxides (SOx), nitrogen oxides (NOx), mercury, and carbon containing species, as well as particulate matter such as dust or fly ash. To meet requirements established under certain laws and protocols, plants that burn fossil fuels subject the resultant flue gas stream to various processes and systems to reduce or eliminate the amount of contaminants present in the flue gas stream prior to releasing the flue gas stream to the atmosphere.
Many flue gas stream treatment systems employ at least one particulate collection device to remove particulate matter from the flue gas stream. One example of a particulate collection device is a fabric filter, through which the flue gas stream flows. The filters include media formed into filter cartridges or filter bags. The particulate-laden flue gas stream flows through the filters while the particulate contaminants are trapped thereon. The filtered flue gas stream is then subjected to another process for further contaminant removal, or is released to the atmosphere.
Over time, the filters collect a significant amount of particulate matter resulting in an accumulated build-up of particulate matter on the filter. The increasing build-up of particulate matter causes an increase in pressure drop across the filters, which in turn increases the energy consumed to generate an effective flow of flue gas through the filters. Accordingly, the filters need to be periodically cleaned to remove the build-up of particulate matter thereon.
A disadvantage of known methods and apparatus to periodically clean the filters is, in case of off-line cleaning, the amount of time it takes to shut down at least a portion of the plant in order to clean the filter(s). Another disadvantage of known cleaning methods and apparatus is the unsynchronized manner in which certain filters have to be cleaned. That is, in plants utilizing multiple filters or multiple filter compartments, the various filter elements may need to be cleaned in a specific order and at a specific time interval. Further disadvantages of known systems and processes include reduced filter life and higher than desired emissions of particulate matter in the released flue gas stream. What is therefore desired is a uniform method by which the filters can be cleaned in an efficient manner that does not disrupt the operation of the plant as a whole and results in longer filter life and lower emissions of particulate matter.